The debris of Russian airliner which is being examined by Russian and Egyptian experts.

The latest US intelligence suggests that the crash of a Russian passenger plane in Egypt was most likely caused by a bomb planted by the terror group Islamic State (IS) or its affiliate, CNN reported on Wednesday.

A US official quoted by CNN said: “There is a definite feeling it was an explosive device planted in luggage or somewhere on the plane.”

The assessment was reached by looking back at intelligence reports that had been gathered before and after Saturday’s crash of the Metrojet Flight 9268 in Egypt’s Sinai that killed all 224 people onboard, CNN quoted the official as saying.

But the official added that there has not been a formal conclusion reached by the US intelligence community on the cause of the crash.

The plane, which was heading to St. Petersburg, Russia, crashed about 23 minutes after taking off from the Egyptian resort city of Sharm el-Sheikh. Most of the passengers were Russian citizens.

There “had been additional activity in Sinai that had caught our attention,” the US official said.

The intelligence regarding the IS is in part based on monitoring of internal messages of the terrorist group, another US official said.

Those messages are separate from public IS claims of responsibility, that official said.

Sinai Province, a militant Egyptian group affiliated with the IS, claimed responsibility for Saturday’s downing of the Russian plane through a statement.

The group has been active in Sinai fighting with Egyptian security forces.

But the claim has not been verified by Egyptian and Russian officials.

US intelligence officials told the media on Monday that infrared US satellite detected a heat flash at the same time and vicinity over the Sinai peninsula where the plane crashed, suggesting an mid-air explosion.